Journals and Posts

My grandmother's Sallie E Gruber (Sallie E Whiteman) reflects her father as unknown on her death certificate. I have searched high and low and find no record of birth with regard to her father - or a birth record for her. She is listed as being born in 1889 in Weissport, PA but there aren't any Whiteman names to be found in PA that could possibly be her father. Do you think my grandmother just took the Whiteman name since she apparently didn't know her real father? I'm at a loss -- what directions should I go next?
Thanks for you help.
Bob Carpenter